1. Field of the Invention
The present invention relates to a control circuit for an air conditioning system of a vehicle, and more particularly to the control circuit for shifting a control mode to a "defroster" mode, activating a compressor of the air conditioning system and indicating its mode, when the "defroster" mode is selected to defrost a front windshield of the vehicle.
2. Description of the Related Arts
A recent model of an air conditioning system for use in a vehicle is provided with all the functions of cooling, heating, dehumidification and ventilation, so that any one of various control modes can be selected by passengers in the vehicle at their own discretion, and also the control mode can be selected automatically in response to temperature in a passenger compartment, or the like. In Japanese Patent Laid-open Publication No.61-75011, it is proposed to ensure a defrosting function when a "heat/defroster" mode is selected in such a condition of relatively high humidity that the windshield is likely to be fogged, as in a raining condition in a cold weather. For this purpose, it is proposed to change an ohmic value of a temperature control resistor in accordance with the selected control mode so as to provide a cooling condition under a minimum temperature, and provide a dehumidification effect by an evaporator as well as defogging effect by air flow. Therefore, a mode detection switch is provided for setting the ohmic value for the temperature control resistor to enable a compressor to operate in the "heat/defroster" mode. Also, in Japanese Patent Laid-open Publication No.63-22724, there is disclosed a demist control apparatus for a vehicle air conditioning system, which is arranged to activate a compressor until a temperature of an evaporator is decreased lower than the freezing temperature thereof, when a "recirculation" mode is selected in a cold weather to cause windows to fog up.
According to the vehicle air conditioning systems as described above, when the "defroster mode" is selected, it is preferable to activate the cooling compressor, so as to blow the air dehumidified by the evaporator to the windshield. In this case, it is preferable that once a passenger simply operates a "defroster" mode switch, the control mode will be shifted to the "defroster" mode automatically, and the compressor will start to operate. Furthermore, it is preferable to indicate operating conditions of those devices, i.e., an indication of the "defroster" mode being selected and that of the compressor being activated (hereinafter, simply referred to as "A/C operating indication" to represent both indications).
With respect to a driving circuit of an actuator or the like for activating the compressor, there is known a control circuit for activating the actuator and indicating the activating condition. For example, Japanese Patent Publication for opposition No. 2-60535 discloses an apparatus which includes a plurality of driving lines connected to each actuator driving circuit, a plurality of indication lines provided in accordance with each driving line for indicating an operating condition of each actuator, and an apparatus for changing an operating condition including a plurality of switches provided in accordance with each driving line and indication line, and which controls the actuator driving circuit by operating each switch so as to control each actuator driving circuit, and indicates the operating condition of the actuator by controlling the respective indication line. In the apparatus as described in the publication, a plurality of switches are provided to constitute the apparatus for changing the operating condition, wherein each switch is formed by a pair of switching sections for switching two terminals respectively, and wherein one terminal of each switching section is connected to the respective driving line or indication line to separate electrically from each other, and an output terminal of each switching section is connected to the other terminal of a pair of switching sections for constituting the switch at next stage, one after another, and finally grounded to the earth.
FIG. 14 illustrates a control circuit which enables the control mode of the vehicle air conditioning system to be shifted to the "defroster" mode by turning a "defroster" mode switch on, and which enables its operating condition to be indicated by the indicator, at the same time. The circuit as shown in FIG. 14 relates to a so-called heater control device, in which a group of terminals to be connected with amplifiers in the air conditioning system are indicated by alphabetical indications encircled and indicated by "AMP" in FIG. 14. The heater control device is a device for shifting an inlet and outlet of the air conditioning system, shifting vents thereof, changing an amount of air flow, controlling a temperature of the air, and so on. According to a recent heater control device, when switches are operated to output electric signals, servomotors installed in the air conditioning system are activated in response to the output signals. The terminals as shown in FIG. 14 are described in detail hereinafter.
First of all, "ILL+" and "ILL-" are terminals connected to a circuit for lightening night illumination lamps (LMP) which are mounted on a heater control panel, or an air conditioner control panel. An on-off switch for closing or opening the circuit is provided as an illumination switch (not shown) in the compartment of the vehicle. Next, a terminal (FACE) is provided for fixing an air outlet to a "Face" mode in which the air flow is directed to a passenger's face. A terminal (B/L) is provided for fixing the air outlet to a "bi-level" mode in which the air is blown into the compartment through an outlet for blowing the air near the passenger's face, and at the same time through an outlet for blowing the air near the passenger's feet. A terminal (FOOT) is provided for fixing the air outlet to a "foot" mode in which the air flow is directed to the passenger's feet. A terminal (F/D) is provided for fixing the air outlet to a "foot/defroster" mode in which the air is blown into the compartment through the outlet for blowing the air near the passenger's feet, and also through the outlet for blowing the air to the inner surface of the front windshield. With each of those terminals (FACE), (B/L), (FOOT) and (F/D) grounded to the earth, a driving signal is fed to each amplifier (not shown).
A terminal (DEF) is provided for fixing the air outlet to a "defroster" mode in which the air flow is directed to the inner surface of the front windshield. When the terminal (DEF) is grounded, a driving signal is fed to an amplifier (not shown). Terminals (A/C+) and (A/C) are provided for activating a compressor of the air conditioning system, and so arranged that when the terminals are electrically connected with each other, a signal for activating the compressor is fed to an amplifier (not shown) of the compressor. This is because it is necessary to prevent the compressor from being activated, when a blower fun motor (not shown) is in "off" condition. Therefore, there may be a case where the compressor will not be activated, even if an air conditioning switch (hereinafter, referred to as A/C mode switch) (6) is turned on. It may be so constructed that the terminal (A/C) is grounded to provide a signal for activating the compressor. A terminal (ACID) is provided for being grounded only when the compressor operates, because the compressor may not be activated even if the A/C mode switch (6) is turned off, as described above. Accordingly, an indicator (LA) will not be lightened unless the compressor operates, even when the A/C mode switch (6) is in "on" condition. The terminal (ACID) may be omitted by grounding it to the earth. A terminal (REC) is provided for fixing the air inlet to a "recirculation" mode in which the air is recirculated in the compartment, while a terminal (FRS) is provided for fixing the air inlet to a "fresh air" mode in which the air is introduced from outside of the compartment. When these terminals (REC), (FRS) are grounded, the signal for activating the corresponding amplifier is fed. A terminal (IG) is connected to a battery (not shown) through a switch co-operating with an ignition switch (not shown), so that when the ignition switch is in "off" condition, the circuit as shown in FIG. 14 is not supplied with the electric power. The terminal (GND) is connected to an earth terminal of the battery (not shown).
A light control circuit (DCT) is connected to the terminal (IG), and includes the indicators (LA), (LD) formed by light emitting diodes (i.e., LED), brightness of which is slightly reduced at night. That is, when the night illumination lamp (LMP) is in "off" condition, a transistor (Trx) which is connected to the terminal (IG) through a diode (Dx) is turned on, so that a relatively high voltage is applied to each of series circuits having the respective indicators (LA), (LD) to lighten them relatively bright. However, when the night illumination lamp (LMP) is in "on" condition, the transistor (Trx) is turned off, so that each of the series circuits having the respective indicators (LA), (LD) is connected to the battery through the diode (Dx), as well as a resistor (Rx) and a diode (Dy) which are connected between the emitter and collector of the transistor (Trx). Therefore, a current fed to each of the indicators (LA), (LD) is reduced to lighten them relatively dark, comparing with those lightened when the night illumination lamp (LMP) is off.
As shown in FIG. 14, a pair of switches are formed to be operated simultaneously, in each of a FACE mode switch (1), B/L mode switch (2), FOOT mode switch (3), F/D mode switch (4), DEF mode switch (5), A/C mode switch (6) and F/R mode switch (7). In each mode switch, a pair of switches are formed of a lock type. Among the mode switches, a self-lock mechanism is formed in the A/C mode switch (6) and F/R mode switch (7). The rest of the mode switches are mechanically connected with each other to form a lock-release mechanism, by which only one of the mode switches (including a pair of switches) is locked to be "on", while other mode switches are not locked. Therefore, in accordance with the normal operation of the mode switches, at least one of them is turned on. However, all the mode switches can be turned off. In such an abnormal case where a pair of mode switches are operated simultaneously, none of the switches can be locked without a particular mechanism to avoid it.
Thus, each mode switch has a pair of switches co-operating with each other (referred to as a first switching section and second switching section), each switch having a pair of fixed contacts and a moving contact for moving to contact with one or the other of the fixed contacts. When each switch is off, the circuit is open, and when each switch is on, the circuit is closed. For example, in the DEF mode switch (5), a fixed contact (Ac) is provided for closing a circuit in switching operation, in other words a fixed contact at "on" side of the first switching section is indicated by (Ac). And, a fixed contact at "off" side of the first switching section is indicated by (Ao). With respect to the second switching section, the fixed contact at "on" side is indicated by (Bc), and the fixed contact at "off" side is indicated by (Bo). Moving contacts for use in the switches are indicated by (Am), (Bm), respectively, as shown in FIG. 14.
In operation, when the DEF mode switch (5) is turned on, the moving contacts (Am), (Bm) of the switches are connected to the fixed contacts (Ac), (Bc) at the "on" side as shown in FIG. 14. As a result, the terminal (DEF) is connected to the terminal (GND) through the fixed contact (Ac), and also transistors (Tr1), (Tr2) are activated to allow a current flow as indicated by an arrow respectively in FIG. 14, so that the terminal (A/C+) is electrically connected to the terminal (A/C) through the transistor (Tr1), and the light control circuit (DCT) is electrically connected to the terminal (ACID) through the transistor (Tr2) and indicator (LA). At the same time, the light control circuit (DCT) is electrically connected to the terminal (GND) through the indicator (LD) and the fixed contact (Bc). Consequently, a drive circuit for actuating the defroster (not shown) is operated, and a drive circuit for actuating the compressor (not shown) is operated, with the indicators (LD), (LA) operated to indicate their operating conditions, respectively.
That is, the aforementioned functions can be performed with the mode switches and terminals provided in the same conditions as in the prior apparatus. However, a pair of switching transistors are needed in the above-described construction, and resistors or the like are needed as well, so that the cost of the apparatus will be raised.